Development hours Vs QA hours

Variable that change ratio of development hours to QA hours.

• Are the QA and Dev teams equivalently skilled between the 2 projects?

• Are the QA and Dev teams equivalently knowledgable between the 2 projects?
  

• In the business envrionment similar between the 2 projects?
  

• Is the Development model similar between the 2 projects?
  

• Is the structure of the 2 projects similar? (testing an engancement to an existing system is a vastly different animal from testing new development)
  

• Are the breakdown of responsibilities for each team the same between the 2 projects?(maybe in 1 Dev handles Configuration Management and deployment, in another QA Does for example)
  

• Do both Projects have similar data requirements? (testing a system which has a large database behind it is vastly different from tesing one with a rudimentary one)
  

• Do both Projects have similar target audiences? (Code intended for trained specialists has different requirements from code intended for the general public)
  

• Do both Projects run in the same sets of operational envrionments? (Hardware, OS, Browser, JDK, .Net Framework, etc.)
  

• Do both projects support the same number of sets of operational envrionments

And that is just off the top of my head I have come up with 10 variables that will vastly change the ratio of development time to QA time and I'm sure there are at least another 10 I've missed.

So really the discussion needs to be not on what percentage of development hours should QA take but rather how do we accurately estimate how long it will take to test a project. We also need to be vigilant and immediately challenge ANYONE who mentions a ratio between Development hours and QA hours in any context except "Well Project X is similar to Project Y and in Project X QA time was Z% of Dev time so in Project Y the Ratio should be close to Z%".